Sinble-channel currents are measured in isolated areas of excitable-cell membranes using the patch electrode method. Channel gating is studied as a stochastic process in cultured rat muscle, mouse spinal cord neurons, and anterior pituitary cells. Gating kinetics are determined for various synaptic agonists and partial agonists acting on the postsynaptic receptors, for electrically excitable channels and for the calcium-induced potassium channel. Modification of channel gating by pharmacological agents and neurotransmitters is studied as a means of establishing a picture of synaptic integration based on the properties of membrane ionic channels.